Leaf spring

ABSTRACT

A leaf spring made of a flat, thin, metallic strip comprised of an elongated flexible member with two parallel sides terminating at either end into flat rectangular, corss-like or circular shapes with a width approximately twice the width of the strip at its midpoint. The ends are crimped or cold pressed downward and then outward near their edges to form flanges. The crimped or pressed ends become each foot of the leaf spring.

BACKGROUND OF THE INVENTION

This invention relates generally to high performance springs, and moreparticularly to leaf springs used in measuring apparatus for very lightmasses and forces.

Mechanical springs used in measuring apparatus for very light masses andforces, such as gem scales and load cells, have stringent sensitivityrequirements. The spring must be highly sensitive to load, and mustaccurately duplicate displacements for various loads. With leaf-typesprings, this requires a very thin leaf member for sensitivity and aflat, rigid spring footing to prevent peeling stresses between the footbottom and the surface it is adhered to, and thereby to insure accuraterepeatability in displacements.

Heretofore, rigidity in the foot of leaf springs has been providedthrough thickness. Either the thin spring member is sandwiched betweentwo thicker members at the foot, or the thin spring member is machinedfrom a thick section making up the spring foot. Either approach hasdrawbacks when applied to leaf springs used in gem scales or load cells,especially of the type disclosed in my copending patent application,Ser. No. 07/018,176, filed 02/24/87, which discloses an electronicbalance for measuring very light masses and capable of correcting anerror in the measured value due to off-center placement of the mass tobe weighed. Essential to the operation of said balance are thedeflection measurements accomplished using a plurality of capacitorsformed between two rigid, closely-spaced plates with specific patternson the plates forming the capacitors. The plates are held apart by threeor more springs Spaced around the periphery of the plates and attachedthereto.

Leaf springs used in measuring apparatus for very light masses have avery thin leaf member. For strength, flexibility, repeatability andsensitivity, the leaf spring member is generally metallic. Because sucha member is highly sensitive to very light loads, i.e., to 0.01 carat,it is also very sensitive to heat. The thicker a metal is, the longer itwill take to thermally neutralize itself when subject to temperaturechanges, whereas a thin metal will neutralize itself quickly to the sametemperature as the surrounding ambient air. Since the characteristics ofmetal change with heat, an apparatus with a thicker leaf spring, i.e.,the leaf spring member or the leaf spring footing, may take up to onehour to thermally neutralize itself after being subject to a temperaturechange.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages of the prior art anddiscloses a leaf spring footing which has the thinness of the leafspring member in its foot, and also has the strength of the prior artleaf spring footings. The thinness of the entire leaf spring permits anapparatus using such a spring to be used much more quickly after atemperature change than has been heretofore possible. The leaf springmember and foot are made from the same thin metal strip. The ends ofeach strip initially are flat polygonal, rectangular, cross-like, orcircular shapes with a width approximately twice the width of the stripat its midpoint. The ends of the strip are then cold pressed in a dieforming a crimped shape along two or more sides of each end. The sidesare crimped downward and then outward near their edges to form flanges.The crimped ends become each foot of the leaf spring. The resultingcontour of the leaf spring footing gives the spring strength while atthe same time maintaining uniform thinness throughout the leaf spring.The flanges provide flat, rigid portions in each spring footing foradhesion by gluing or other means to a surface, thereby substantiallyreducing the peeling stresses on the adhesive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are plan and side elevational views, respectively, of athin metal strip before formation into the leaf spring of the presentinvention.

FIGS. 2A, 2B and 2C are plan, side elevational, and perspective views,respectively, of one embodiment of the leaf spring of the presentinvention.

FIGS. 3A and 3B are perspective views from the front and rear,respectively, of the leaf spring footing of the embodiment illustratedin FIGS. 2A, 2B and 2C.

FIGS. 4A, 4B and 4C are plan, side elevational, and perspective views,respectively, of another embodiment of the leaf spring of the presentinvention.

FIGS. 5A and 5B are perspective views from the front and rear,respectively, of the leaf spring footing of the embodiment illustratedin FIGS. 4A, 4B and 4C.

FIGS. 6A and 6B are plan and side elevational views, respectively, of athin metal strip before formation into another embodiment of the presentinvention.

FIGS. 7A, 7B and 7C are plan, side elevational, and perspective views,respectively, of another embodiment of the leaf spring of the presentinvention using the strip of FIGS. 6A and 6B.

FIGS. 8A and 8B are perspective views from the front and rear,respectively, of the leaf spring foot of the embodiment illustrated inFIGS. 7A, 7B and 7C.

FIGS. 9A, 9B and 9C are plan, side elevational, and perspective views,respectively, of still another embodiment of the present invention usingthe strip of FIG. 6.

FIGS. 10A and 10B are perspective views from the front and rear,respectively, of the leaf spring foot of the embodiment illustrated inFIGS. 9A, 9B and 9C.

FIG. 11 is an exploded perspective view of a section of an apparatususing the leaf spring of FIGS. 7 and 8.

FIG. 12 is a perspective view of a section of an apparatus using theleaf spring of FIGS. 7 and 8.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings in detail, wherein like numerals refer to likeelements, reference numeral 1 refers to the leaf spring of the presentinvention. FIG. 1 illustrates a flat, thin strip 10 in plan view (FIG.1A) and side elevation (FIG. 1B) formed into an elongated flexiblemember 15, with two parallel sides 17, terminating at either end 20 in agenerally flat, cross-like shape with a first width from edge 21 to edge21 transverse to the longitudinal axis of the member 15 approximatelytwo to three times the width from side 17 to side 17 of said member 15,and a second width from side 22 to side 22 transverse to thelongitudinal axis of the member 15 approximately one to two times thewidth from side 17 to side 17 of said member 15. In the embodimentsdescribed herein, the strip 10 is metallic. However, the strip 10 couldalso be made of other materials such as ceramic, quartz, etc.

As may be best understood from FIGS. 2A, 2B, 2C, 3A and 3B, thecross-like shaped ends 20 are crimped downwardly and outwardly to formthe spring footings 25. Specifically, a portion of each element 30, 31and 32 forming the cross-like shaped end 20 of FIG. 1A is bentdownwardly and outwardly. Elements 30 and 32 are bent along linesparallel to the longitudinal axis of the member 15 and extending fromthe edges 22, downwardly at an approximate 90° angle to the undersurface11 of the strip 10, and then outwardly 90° forming two flanges 27 havinga longitudinal axis and running in a plane parallel to the longitudinalaxis and plane of the member 15. The edges 21 now form the outer edge ofthe flanges 27 and are parallel to the member sides 17. The thirdelement 31 is bent along a line transverse to the longitudinal axis ofthe member 15 and extending between the edges 23 at right angles to theedges 21 and 22, downwardly at an approximate 90° angle to theundersurface 11 of the strip 10 and then outwardly 90° forming a flange28 having a longitudinal axis transverse to the longitudinal axis of themember 15 and running in a plane parallel to the plane of the member 15.In this embodiment of the invention, the leaf spring foot 25 extendsgenerally downward from the elongated member 15 although still apiecewith the member 15. The shaping of the footing 25 as described aboveprovides strength while at the same time maintaining the thinness of theleaf spring elongated flexible member 15 throughout, the member 15 beingthe spring element of the leaf spring 1. The flanges 27 and 28 provide aflat, rigid structure in the foot 25 for adhesion to a surface therebysubstantially reducing peeling stresses. Two cuts 24 are made extendinginto the strip ends 20 on a line extending from the member sides 17. Thepurpose of these cuts 24 is to move the effective force on the footing25 from the spring element 15 toward the middle of the footing 25thereby further reducing the peeling effect on the flanges 27. Theprimary purpose of forming the flange 28 is to provide transverserigidity to the footing 25. The flange 28 itself may be eliminated aslong as the downwardly extending wall 26 remains. When installing thisembodiment of the leaf spring 1, such as may be seen in the perspectiveview of FIG. 2C, the elongated member 15 has a slightly upwardly curvingshape at the footing 25. This is done to prevent opposite curvature ofthe flexible member 15 and ensure linearity. In this example, twocapacitor plates 50 and 51 are held between several leaf springs 1 ofthe present invention, such as in the gem scale described in detail inmy copending application, Ser. No. 07/018,176, filed 02/24/87, referredto above. The upper capacitor plate 50 is held by one foot 25 of eachleaf spring 1. Specifically, the flanges 27 and 28 of the foot 25 areglued to the plate 50. The spring elements 15 of each spring 1 are thenbent around and below the bottom capacitor plate 51 so that the otherfoot 25 of each spring 1 may be attached to the bottom capacitor plate51. Again, the flanges 27 and 28 of the foot 25 of each spring 1 areglued to the plate 51.

The advantages to the embodiment described above are that it isrelatively easy to make, provides thinness of the leaf spring element 15throughout, and provides a strong footing 25 with excellent resistanceto peeling stresses between the leaf spring's foot bottom, i.e., flanges27 and 28, and the surface, e.g., 50, 51, it is adhered to.

FIGS. 4A, 4B, 4C, 5A, and 5B illustrate another embodiment of theinvention. This leaf spring 1 is formed in essentially the same manneras the above described embodiment, but installation of the leaf spring 1is different. As may be best understood by comparing FIG. 2B to 4B, andFIG. 2C to 4C, the flexible member 15 is bent back over the footing 25instead of directly extending from the footing 25 as was the case withthe first embodiment. In the first embodiment of the leaf spring 1, thefoot 25 is more directly related to the flexible member 15. The secondembodiment has a double spring action for more vertical force effect onthe foot 25. Because the first embodiment has less parallel motion,there will be a rotary stress on the glue adhering the flanges 27 and 28to the surfaces 50 and 51. The bent over design of the second embodimentdecreases rotary action and, therefore, less stress is put on the glue.Although mechanical creep, i.e., stress-time effect, is always present,there is less in the second embodiment because of the double springaction of the reconfigured leaf spring 1.

In still another embodiment of the invention, as shown in FIGS. 6A, 6B,7A, 7B, 8A and 8B, the ends 20 of each strip 10 initially are flatrounded shapes with radial diameters approximately twice the width ofthe member 15 at its midpoint. The centers of the rounded ends 20 of thestrip 10 are then cold pressed in a die concentrically forming a domicalcontour 37 in each rounded end with a residual flange 38 about the edgeof the dome 37. Each rounded end 20 is cut in a line 35 on either side17 of the elongated member 15 to a depth into each rounded end 20 nearto an apex 36 formed by the domical contour 37. The elongated member 15lies flat in a plane nearly touching the apexes 36 of the domicalcontour 37 of each end 20. The leaf spring foot 25 is, therefore,generally positioned for the most part below the elongated member 15although still apiece with the member 15. The domical contour 37 of thespring footing 25 provides strength while at the same time maintainingthe thinness of the leaf spring elongated member 15 throughout theentire leaf spring 1. Although the first two embodiments of the leafspring have superior mechanical creep characteristics, the domicalembodiment with its continuous residual flange 38 has more all-aroundglue surface and provides, thereby, a stronger footing 25.

As was illustrated in the first two embodiments, the leaf spring 1described immediately above may be installed so that the elongatedmember 15 is bent back over the footing 25 instead of directly extendingfrom the footing 25 as was the case with the embodiment describedimmediately above. FIGS. 9A, 9B, 9C, 10A and 10B most clearly illustratethis. This embodiment provides also a double spring action for a morevertical force effect on the footing 25. This configuration will alsohave less mechanical creep than the embodiment described immediatelyabove.

FIGS. 11 and 12 illustrate the invention 1 in use. In this applicationused in a gem scale, two capacitor plates 50 and 51 are held betweenthree leaf springs 1 using the invention embodiment illustrated in FIGS.7A, 7B, 7C, 8A and 8B. The upper capacitor plate 50 is held by one foot25 of each leaf spring 1. The member 15, i.e., spring element, of eachspring 1 is then bent around and below the bottom capacitor plate 51 sothat the other foot 25 of each spring 1 may be attached to the bottomcapacitor plate 51. The springs 1 in this application will quicklyattain thermal neutralization after temperature changes due to thesprings' uniform thinness throughout.

It is understood that the above-described embodiment is merelyillustrative of the application. For example, the cross-shaped ends 20in FIGS. 1A and 1B may be rectangular and element 31 eliminated,resulting in a two-flanged 27 spring footing 25. The ends 20 may alsoeach have a polygonal shape, providing a compromise of features betweenthe rectangular/cross-shaped end embodiments and the rounded endembodiments. The polygonal shape would have four or more edges and wouldbe formed into footings with four or more sides having multiple flanges.The elongated flexible member 15 of any embodiment may also be stiffenedwithout sacrificing thinness. Slight corrugations may be added to theelongated member 15 for a stiffer spring element. Although the aboveembodiments used as a preference metal strips, the strip 10 could becomprised of other materials such as ceramic or quartz, or combinationsthereof of metal, ceramic or quartz. Other embodiments may be readilydevised by those skilled in the art which will embody the principles ofthe invention and fall within the spirit and scope thereof.

I claim:
 1. A leaf spring used in measuring masses and forces, comprisedof:a flat, thin strip formed into an elongated flexible memberterminating at either end into rectangular, cross-like shapes with anoverall width greater than the width of the elongated member whereineach end has three elements forming the cross-like shaped end, of whichtwo are side elements and the third is a middle forward element andwherein said side elements are bent downward along lines parallel to thelongitudinal axis of said elongated flexible member and then outwardnear said outer side edges to form flanges.
 2. A leaf spring inaccordance with claim 1 wherein:each end is cut in a line on either sideof the elongated member part way into each end approximately to a pointparallel to a midpoint of said outer side edges.
 3. A leaf spring inaccordance with claim 1 wherein:said middle forward element has aforward outer edge transverse to the longitudinal axis of the elongatedflexible member.
 4. A leaf spring in accordance with claim 3wherein:said middle forward element is bent downward along a linetransverse to the longitudinal axis of said elongated flexible memberand extending from the foremost points of said outer side edges.
 5. Aleaf spring in accordance with claim 4 wherein:said middle forwardelement is bent outward near said forward outer edge to form a flange.6. A leaf spring in accordance with claim 5 wherein:said flanges formedfrom said three elements lie in a plane generally parallel to the planein which the elongated flexible member lies flat.
 7. A leaf spring inaccordance with claim 6 wherein:said strip's formed ends are the leafspring's footings.
 8. A leaf spring in accordance with claim 7wherein:said side elements have outer side edges parallel to thelongitudinal axis of the elongated flexible member.
 9. A leaf spring inaccordance with claim 6 wherein:the thinness of the strip is uniformthroughout the elongated flexible member and footings.
 10. A leaf springin accordance with claim 9 wherein:said strip is made of metal.
 11. Aleaf spring in accordance with claim 10 wherein:said leaf spring isinstalled such that said elongated flexible member is bent back over oneor more said footings.
 12. A leaf spring in accordance with claim 11wherein:said elongated flexible member has slight corrugations forstiffness.
 13. A leaf spring in accordance with claim 10 wherein:saidelongated flexible member has slight corrugations for stiffness.